Bits of information about Scotch single malt whisky, its production, history and chemistry.

Saturday, June 11, 2011

Lavender in whisky. A conspiracy of French women, British brewers, Peruvian distillers and hot condensers?

Lavender

The flowery perfumy notes in whisky have been widely discussed in various forums for years. In short, some whisky drinkers have experienced very strong off-notes of lavender soap in several whiskies. Especially the flowery notes of Bowmore and Glen Garioch distilled in the early 1980s have been noted.

Lavandula angustifolia

Lavender (Lavandula) is a genus of flowering plants common in mediterranean region. There are ~39 species of lavender; the most common are Lavandula angustifolia (English lavender, common lavender, narrow leaf lavender), Lavandula stoechas (French/Spanish lavender, topped lavender), Lavandula dentata (French lavender) and Lavendula latifolia (spike lavender, broad leaf lavender, Portuguese lavender). To make things complicated the English lavender is not native to England but to western mediterranean; the French lavender (L.dentata) is native to Spain, Canary islands and Madeira. Most of the cultivated French lavender is either L.angustifolia or a more productive hybrid of L.angustifolia and L.latifolia called lavandin (Lavandula x intermedia or L.hybrida).

The odor active compounds in lavender essential oil are primarily terpenes and their oxygenated derivatives. The essential oil of L.angustifolia is the most appreciated, described as lavender, lime tree, coriander and flowers. Lavandin (L.x intermedia) oil is much cheaper, but the odor has more soap, camphor, turpentine, artificial fruit, fat and eucalyptus. L.latifolia essential oil is even harsher with more camphor, menthol and eucalyptus. In fact coriander essential oil is closer to L.angustifolia oil than the oil of L.latifolia. In table below are percentages of odor compounds found in typical essential oils of L.angustifolia, L.latifolia and lavandin (L.x intermedia). Linalool (aka β-linalool, linalyl alcohol, linaloyl oxide, p-linalool, allo-ocimenol, 2,6-dimethyl-2,7-octadien-6-ol, licareol, coriandrol) and its derivatives are responsible for the flowery lavender scent. Often linalool is added to lavandin oil and other perfumes to soften the odor. Up to 80% of perfumed hygiene products (soaps, shampoos, perfumes etc) contain linalool, often added as a fragrance. The odor treshold for linalool is usually very low, about 0,8-7,4 ppb, depending on the stereoisomer structure. Usually oxidation of linalool compounds adds to the odor.

L.angustifolia

L.latifolia

L.x intermedia

linalool

31

3

20

linalyl acetate

16

4

25

camphor

3

32

11

1,8-cineol(eucalyptol)

na

39

na

Table1. Essential oil compounds from different lavenders.

Monoterpene metabolism by yeasts (King 2000)

Let's assume that linalool (and/or linalyl acetate) is responsible for the lavender aroma in some whiskies. Why would some distillates contain more linalool than others?

Linalool is produced by various plants, especially by lavender and most herbs such as mints, coriander, laurels and cinnamon. Hops used in beers (Cascade hops especially) are also quite rich in linalool and sometimes hops impart a flowery odor to finished beer, especially if the hops are added after the boiling. Many brewers yeasts also affect the metabolism of monoterpenes (see picture above). Beer is usually boiled in mashing, which diminishes the linalool content considerably via evaporation (This is probably why hopped beer on a frying pan smells of lavender, see Dave's e-pistle). However, in distillery mashing the wort is not boiled and the linalool in a distillery wort would be carried into the distillate if hopped wort was used in distillation (I know, this is just about as likely as the urban legend about scented soap used in distillation).

Another possible source for linalool in wort is yeast or fungi. Distiller's yeast does not usually produce significant amounts of linalool, but brewer's yeast (both lager and ale) and some lactic acid bacteriae (Kluyveromyces lactis) do and additionally there are some mutations of Saccharomyces that produce over ten times more linalool and geraniol than ordinary fermentation yeasts. These yeasts have been used in brandy fermentations and probably in production of aromatized wines such as sweet muscat. Whether this kind of yeast strain might have been used in one or two Scotch whisky distilleries in the 1980s is extremely unlikely, but brewer's yeast has been used in many distilleries along with the distiller's yeast. Linalool concentration of wort increases as the fermentation time gets longer. Too long fermentations with brewer's yeast would probably add considerably to the linalool content of the wort. A sporadic yeast mutation, a contaminant wild yeast strain, excessive lactic bacteria growth (due to prolonged fermentation time) or a fungal infection in wort would also produce too much linalool.

Distillation affects the linalool concentrations of the spirit. It is possible that overheating the still and burning the wash might convert some other terpenes to linalool. The amount of reflux and condenser temperature is probably even more important. To understand a bit more about linalool and distillation we should investigate pisco brandy. Pisco is a wine brandy distilled in Peru and Chile. It is batch distilled from muscat wine in ~1500l copper stills (not too different from Scotch malt whisky stills). The pisco distillers try to produce very floral spirit with lots of monoterpenes, especially linalool, which is considered a quality marker for an aromatic high-end pisco together with geraniol and nerol. Pink muscat and muscat of alexandria grapes are very rich in linalool and therefore used as a component in the wine blend, but usually also cheaper and less fragrant muscat varieties and pedro ximénez grapes are used to increase ethanol-yield. Pisco contains about ten times more linalool than the average cognac. Ester- and aldehyde- concentrations are also quite high resulting to very fragrant, floral and fruity spirit. The distillation practice and especially the cooling of the condenser is critical in producing linalool-rich spirit; usually the heads fraction is distilled without cooling the condenser, apparently to get rid of the methanol and other high volatiles quite fast without losing much linalool. The boiling point of linalool is 199°C, but since it is poorly soluble in water, it distills quite early in the run along with the alcohols. Linalool is rich in the early stages of the heart run, decreasing slightly towards the tails. Cooling the condenser fast after the heads fraction and allowing much less cooling at the middle of the heart run produces more linalool, although towards the end of the spirit run the cooling is increased to prevent the tails (especially octanoic acid) getting into the spirit.

This might support Dave Broom's speculation about the two-part condensers not working properly in the distillation. If there was an inadequate amount of cooling water in circulation of the condenser, the cooling rate and the reflux at the first part of the heart would be fine, but later in the cut the cooling rate would drop too much. This would probably produce more linalool and other monoterpenes, but also early tails. If a distiller in this case would cut the heart early to avoid the tails in the spirit, the resulting heart fraction would probably be very rich in linalool. Alternatively, if the tails cut was made by timing the run or by the ABV% (opposed to smelling), it would probably become very feinty (and floral).

Pisco

The casks might also be to blame. Fungal infection in the caskwood might be a source for monoterpenes, probably in a winery supplying the casks, as spirit (bourbon or scotch) would likely kill most fungi. Muscat wine casks are not a likely option for excess linalool and pisco is not traditionally matured in oak.

So: IF there was some excess linalool in the wash AND IF the condensers were cooled inadequately in the latter part of the spirit run, there MIGHT be excessive linalool in the spirit producing heavy aroma of lavender. The source of linalool might be hops, an odd yeast strain, brewer's yeast used together with too long fermentation times (my guess) or a fungal infection of the wort. The two-part condensers installed in early 1980s and not working (or used) properly might account for the distillation/cooling part of the problem.

Now, please do not shoot me for this speculation as this is most certainly not science, but merely (mis?-)educated guesswork. Any criticism and conversation on this FWP-phenomenon is very welcome. And for the record: I am apparently not too sensitive to the lavender smell in the Bowmores of 1980s nor in perfumes or flowers. I do get some lavender notes in the 1980s Bowmores but nothing too offensive.